Vegetable crop rotation

Beginning gardeners are told to rotate vegetable crops each
year for insect and disease prevention. That tells them the what, when, where,
and why but sometimes leaves them fuzzy about which crop should follow another
and which crop shouldn't.

Rotation can be complicated. I know one farmer on a 27 year rotation. I
won't plan that far ahead for vegetables.

An average home gardener needs to learn four major families. They are the
mustard family, the bean family, the gourd family and the nightshade family.
All a gardener has to do is move the crops so that members of the same family
don't get planted in the same area year after year.

There are two ways to learn which vegetables belong to which family. You can
keep the list below or you can learn how the flower looks.

Learning how to look at a flower is not simple but just counting the petals
is a start. The only common garden plants with four petals are in the mustard
family which are better know as the brassicas. This includes a bunch of
different types of mustard, cress, cressy, kale, kohlrabi, cabbage, broccoli,
cauliflower, turnips, radish (including diakon), spinach, and rutabaga. Some
uncommon members are Pak-choi, wallrocket, rocket salad, maca, and wasabi.

The lily family is not a major concern when planning a rotation. I will
separate them here because they are the only major vegetable family with 6
flower petals. Asparagus is a member of the lily family but it is a permanent
plant that isn't moved every year. Daylilies are seldom grown for food but they
wouldn't get moved either. Some people put onions in the lily family. Other
people separate them into their own family. Even if we didn't know what the
flower looked like, we can still recognize onions by smell or leaf shape. Chives,
shallots, onions, and garlic are all in this family. I don't personally know
kurrat and rakkyo but they are in this family also. In my garden I don't worry
about rotating this family. The major problem we have on these crops is thrips
which are not controlled by rotation. In the wild you see garlic living several
years in the same spot. I have garlic and chives in fairly permanent locations.
I don't anticipate problems on either of these.

Most of the other common garden vegetables have five petals. Still the bean
family, also know as the legume family, is easy to recognize. I can't describe
a bean flower in a news column but will mention one aspect. Most garden
vegetables have a flower that can produce a mirror image if cut several
different ways. Beans flowers are not like this. Bean flowers have to be cut
just right to produce a mirror image. I don't know a simple word for this.
Zygomorphic is the correct term. Bi-lateral symmetry is longer but may be
easier to understand. The only other vegetables I know with bilateral symmetry
are in the violet family or the mint family. None of these are common in our
local vegetable gardens.

If you are not comfortable recognizing the bean flower, you can go by name.
This is a huge family, but most members are called either beans or peas.
Peanuts are also in this family. Groundnuts, jimica and fenugreek are beans.

There is enough difference in insect and disease pressure between the
peanuts, the Southern peas and the other beans that a gardener could be divide
them into three separate groups. If the gardener separated the beans, they
could plant either peas or beans as a quick summer cover crop without messing
up the rotation. The southern pea group would contain moth bean, adzuki bean ,
black gram, mung bean, Madasgascar groundnut, rice bean, catjang, and yardlong
bean or asparagus bean. Peanuts would be a separate group. Everything else in
the bean family would be lumped together in another group.

In part 2 I will cover the final two major vegetable groups.

Part 2

In my vegetable garden I have a minimum three year rotation.
That isn't quite enough for melons and cantaloupes but more than enough for
some crops. With a good fertility program a person could grow sweet corn
several years in the same spot, but since the other crops must move, the sweet
corn gets pushed around too.

Commercial farmers also consider the fertility program when planning a
rotation. Some rotation programs try to put a heavy feeder behind a legume crop
to take advantage of residual nitrogen the beans fix out of the air. If you
were going to manure every third year you would place sweet potatoes the third
year. This puts it as far as possible time wise away from the manure
application. Irish potatoes should be the third year after liming if possible.
Varying early and late crops will also help break weed populations.

Basically, I wouldn't worry about those criteria. I simply group plants into
4 major families and make sure members of the same family don't follow year
after year.

Last week I mentioned the brassicas with 4 petal flowers, the lilies with 6
petal flowers and the beans with zygomorphic (a mirror image in one plane)
flowers. That leaves the cucurbit family also known as the gourd family and the
nightshade family. At first glance, there is surprisingly little difference
between the flowers of these two groups. Both have five petals. Other parts of
the flower are similar. The major difference is that nightshade plants always
have the ovary above the petals while ovaries in the gourd family are always
below the petals. Again if you fill uncomfortable remembering this just keep a
list.

Solanaceae is commonly called the nightshade family. Peppers, Potatoes,
Tomatoes, and eggplants are common members of this family. Tamarillo,
tomatillo, rocoto, box thorn, golden apple (solanum aethiopicum), American
black nightshade, Chinese lantern, cape gooseberry, gilo, and sweet pepino are
uncommon members of this family. Tobacco and petunias are in this same family
but we generally don't grow them in the vegetable garden. Some personal
experience indicates hot peppers may not need as much rotation but if
everything else it moving, it is simple enough to move the hot peppers also.